Physicists have achieved a remarkable feat by inflating atoms to hundreds of times their usual size, creating a spectacular version of exotic matter known as a time crystal. This peculiar state of matter, previously thought to be impossible, was realized by bombarding rubidium atoms with lasers, causing them to expand into an excited form. This breakthrough opens up exciting possibilities for delving deeper into the properties of time crystals, which exhibit a unique periodic oscillation between two states without ever losing energy. The new technique, detailed in the July 2nd edition of the journal *Nature*, could also play a pivotal role in the development of more powerful quantum computers.
The concept of time crystals, first proposed in 2012 by Nobel laureate physicist Frank Wilczek, involves groups of particles that repeat their behavior in time, much like ordinary crystals (such as table salt or diamonds) exhibit spatial repetition. This phenomenon is captivating to physicists because it challenges the conventional understanding of symmetry in the laws of physics, which are typically symmetrical across both space and time, resulting in outcomes that are consistent regardless of direction. Crystals, however, break this symmetry by aligning themselves in a specific spatial direction. This means that even though the fundamental laws of physics remain symmetrical, the outcomes they produce are influenced by the direction in which they act upon the crystals. Similarly, time crystals break symmetry in time. They exist in the lowest possible energy state permitted by quantum mechanics and oscillate between two states without slowing down.
The extraordinary properties of time crystals have led to speculation about their potential as perpetual motion machines, seemingly defying the second law of thermodynamics. However, this is not the case. These crystals, driven by lasers, are incapable of losing or gaining energy. The laser light simply triggers the two-step oscillation, and as with many systems containing only a few atoms, the second law of thermodynamics does not apply to them. Numerous time crystals have been created since Wilczek’s initial proposal, each offering unique insights into this peculiar phase of matter.
To construct their time crystal, the researchers behind the new study utilized rubidium atoms excited into what are known as Rydberg states. By directing laser light onto a glass container filled with rubidium atoms, the physicists infused the gas with a significant amount of energy. The laser light stimulated the electrons within the atoms, causing the distance between the atomic nuclei and the electrons’ outer shells to expand dramatically, becoming hundreds of times their original size. This expansion led to an intriguing phenomenon. “If the atoms in our glass container are prepared in such Rydberg states and their diameter becomes huge, then the forces between these atoms also become very large,” explained co-author, a physicist at the University of Vienna. “And that in turn changes the way they interact with the laser. If you choose laser light in such a way that it can excite two different Rydberg states in each atom at the same time, then a feedback loop is generated that causes spontaneous oscillations between the two atomic states. This in turn also leads to oscillating light absorption.” Essentially, a time crystal emerged within the glass container. “This is actually a static experiment in which no specific rhythm is imposed on the system,” the physicist added. “The interactions between light and atoms are always the same, the laser beam has a constant intensity. But surprisingly, it turned out that the intensity that arrives at the other end of the glass cell begins to oscillate in highly regular patterns.”
The researchers are now dedicated to further exploring the capabilities of their newly created time crystal and testing its potential applications. They suggest that it could be employed to develop highly sensitive sensors and contribute to a better understanding of quantum synchronization, a phenomenon where multiple quantum systems act in unison. This understanding could be instrumental in the development of more advanced quantum computers.
